Whitefly and whitefly-borne viruses in the tropics : Building a ... - cgiar

Biological Control of Whiteflies by Indigenous Natural Enemies
Parasitoids (40 plugs)
60
50
40
30
20
10
0
Bemisia
tabaci
Trialeurodes
vaporariorum
Amitus Encarsia Eretmocerus
Metaphycus Signiphora
Figure 8. Relationship between parasitoid
complex and whitefly species
collected from several crops in the
departments of Atlántico, Córdoba,
Caldas, Quindío, Risaralda and
Valle del Cauca, Colombia.
of Amitus, indicating that Encarsia may
have acquired a degree of resistance to
some of the pesticides applied.
Parasitism studies with
E. hispida
Of the three methodologies evaluated,
the highest rate of parasitism was
obtained using the third method.
Parasitism levels using the first two
methods were low. The highest rate of
parasitism with method 1, the use of
nylon-mesh cages, only reached 9% in
the third instar. This improved with the
second method (the use of leaves
enclosed in petri dishes) to 30% in the
2 nd instar and to 20% in the 3 rd .
The employment of muslin bags, as
described in the third methodology,
gave the best results. In the first of two
experiments using this methodology,
parasitism rates reached about 75% in
the third instar and 16% in the
1 st instar, 45% in the 2 nd instar and
43% in the 4 th instar (Figure 9). Results
of a second experiment were similar,
with about 75% parasitism in the third
instar and 19% in the 1 st instar, 61%
in the 2 nd instar and 25% in the
4 th instar (Figure 9). The average
parasitism rate for these two
experiments were about 45%, whereas
average parasitism rates were only 6%
using methodology 1 and were 20%
using methodology 2.
% parasitism
80
70
60
50
40
30
20
10
0
I II III IV
Instars
Exp. 1 Exp. 2
Figure 9. Cassava whitefly (Aleurotrachelus
socialis) instar preference by the
parasitoid Encarsia hispida in two
greenhouse experiments.
These results also show that the
third whitefly instar is preferred for
parasitism by E. hispida. An average of
all four experiments resulted in a
parasitism rate of 21% for the
1 st instar, 35% for the 2 nd instar, 46%
for the 3 rd instar and 22% for the
4 th instar. However, the average of the
two experiments using methodology 3
(muslin bags) is 17% for the 1 st instar,
53% for the 2 nd , 75% for the 3 rd and
34% for the 4 th instar. The highest
parasitism rate is in the 3 rd instar,
followed by the 2 nd , 4 th and 1 st instar.
The time period for optimal
parasitoid activity was evaluated using
the third methodology described.
Percent parasitism evaluations were
made at 48, 72, 96 and 216 hours after
parasitoid release. Peak parasitism
activity occurred between 72 (35%
parasitism) and 96 hours (33%
parasitism) (Figure 10). However, even
321